The present invention relates to a method for reducing interference signal influences on a high-frequency measurement device, and also to a corresponding high-frequency measurement device.
High-frequency measurement devices, which, for example, operate in accordance with the radar principle, are used, among other things, for locating objects in walls, roofs, or floors in order to avoid consequential damage caused by drilling, for example. Other potential uses for such devices include locating structural defects such as air pockets in the concrete or comparable defects in the material homogeneity of concrete coverings in bridges. These devices, which can also be embodied in the form of capacitive measurement devices, are likewise used in security technology in the context of area monitoring in order to supervise the presence or precise position of people. It is thus possible in the context of police or military uses, to locate people through a wall.
Another possible use for measurement devices of this kind is high-frequency distance measurement of the type used, for example, in the automotive field as parking assistance devices or driver assistance systems. This kind of high-frequency measurement devices can also be used for distance measurement in the construction field, for example for interior work in buildings. In this connection, it is in particular possible to produce hand-held distance measurement devices for manual laborers. The frequency range in which all of these devices are customarily operated lies between several hundred megahertz and over 100 gigahertz, i.e. in the microwave range.
Even in the range from 1 to 5 GHz, however, an increased amount of interference occurs, for example due to mobile telephones (GSM, GPRS, UMTS, DECT), wireless networks (WLAN, Bluetooth, wireless DSL) or microwave ovens. These interference sources reduce the quality of measurements of the above-mentioned high-frequency measurement device significantly or render measurement completely impossible. Consequently, it is no longer possible to prevent erroneous measurements that result in material damage and/or personal injury.
Previously used methods for avoiding erroneous measurements can in fact eliminate some interference sources through adroit collection of measurement data, but this is only with the presence of a few interference sources, which, in addition, must mostly also be active at the same time. These methods, however, fail to work when newly developed interference sources such as new radio technologies come into use.
DE 102 07 424 A1 has disclosed a method and device for locating enclosed objects, with which at least one captive sensor device generates a detection signal, which travels into the medium to be tested so that an evaluation of the detection signal, in particular through an impedance measurement, makes it possible to obtain information about objects enclosed in the medium. In the method disclosed in DE 102 07 424 A1, a measurement frequency in the GHz range is used in order to generate sufficiently large changes in the measurement signal, even for extremely low capacitance changes caused by the presence of an object enclosed in the medium. In the case of plastic pipes, an inclusion signal imparted by dielectrical inclusions typically lies in the sub-picofarad range so that these small changes in the capacitance to be measured, with an alternating voltage of for example one volt applied to the capacitive sensor and a measurement frequency of 100 kHz, result in differences in the displacement current of less than one microampere.
With the device in DE 102 07 424 A1, a device internal reference measurement is used in order to determine the level of external EMC interferences of the kind, for example, caused by nearby transmitters. Such EMC interferences can be subsequently calculated from an instantaneous measurement signal using the method from DE 102 07 424 A1.
DE 102 33 835 A1 has disclosed a method for eliminating interference from measurement signals that have been corrupted by pulsed interference signals with a known or determinable interference pulse interval. An elimination of the interference from interference sources that transmit in pulse-like fashion is achieved with the method according to DE 102 33 835 A1 in that at least three successive individual measurement values are recorded, with time intervals that differ from the interference pulse interval, and an interference-free measurement value is determined from the at least three individual measurement values.